Wireless Sensor Networks (WSN) are emerging as a new tier within the IT scheme and a rich domain of active analysis involving hardware and system design, networking, and programming models, data management, security and social actors. Wireless sensor networks are compared with wired networks are additional well vulnerable to attacks and intrusions. The intrusion detection is outlined as a mechanism for a WSN to detect the existence of inappropriate, incorrect, or abnormal attackers. The watchdog mechanism is defined to evaluate whether a node has abnormal behaviour in method of forwarding data. Using this Watchdog Algorithm, the intrusions in the network and monitoring multiple misbehaved nodes. Using this algorithm we can realize intruders and reduce the detector rate, and reduce generator value also will increase in throughput. In this paper, we discuss the watchdog based Intrusion Detection System (IDS) provides various kind of attacks in the Wireless Sensor Network.